#include <fstream>
#include <vector>
#define NMAX 100002
#define MMAX 500002
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
struct muchie
{
    int x,y;
    bool uz;
}LM[MMAX];
vector<int>LA[NMAX];
int n,m,S[MMAX],vf,poz;
int sol[MMAX];
void citire();
bool grade();
void gen();
void afisare();
int main()
{
    citire();
    if(!grade())
    {
        fout<<"-1";
        return 0;
    }
    gen();
    afisare();
    return 0;
}
void citire()
{
    int i;
    fin>>n>>m;
    for(i=1;i<=m;i++)
    {
        fin>>LM[i].x>>LM[i].y;
        LM[i].uz=0;
        LA[LM[i].x].push_back(i);
        LA[LM[i].y].push_back(i);
    }
}
bool grade()
{
    int i;
    for(i=1;i<=n;i++)
        if(LA[i].size()%2)
            return 0;
    return 1;
}
void gen()
{
    int crt,urm;
    S[1]=1;
    vf=1;
    while(vf>0)
    {
        crt=S[vf];
        if(LA[crt].size()==0)
        {
            sol[++poz]=crt;
            vf--;
        }
        else
        {
            urm=LA[crt].back();
            LA[crt].pop_back();
            if(LM[urm].uz==0)
            {
                LM[urm].uz=1;
                if(LM[urm].x==crt)
                    S[++vf]=LM[urm].y;
                else
                    S[++vf]=LM[urm].x;
            }
        }
    }
}
void afisare()
{
    int i;
    if(poz-1!=m)
        fout<<"-1";
    else
        for(i=1;i<poz;i++)
            fout<<sol[i]<<' ';
}